6-(3,5-Dimethyl-1H-pyrazol-1-yl)-2,2'-bipyridine as ligand for actinide(III)/lanthanide(III) separation

Denise Girnt; Peter W Roesky; Andreas Geist; Christian M Ruff; Petra J Panak; Melissa A Denecke

doi:10.1021/ic101309j

6-(3,5-Dimethyl-1H-pyrazol-1-yl)-2,2'-bipyridine as ligand for actinide(III)/lanthanide(III) separation

Inorg Chem. 2010 Oct 18;49(20):9627-35. doi: 10.1021/ic101309j.

Authors

Denise Girnt¹, Peter W Roesky, Andreas Geist, Christian M Ruff, Petra J Panak, Melissa A Denecke

Affiliation

¹ Institut für Anorganische Chemie, Karlsruher Institut für Technologie, Engesserstrasse 15, 76131 Karlsruhe, Germany.

PMID: 20849125
DOI: 10.1021/ic101309j

Abstract

With the aim of better understanding the selectivity of the established system 2,6-ditriazinylpyridine (BTP) for actinide(III)/lanthanide(III) separations, a related model system was synthesized and studied. The N donor complexing ligand 6-(3,5-dimethyl-1H-pyrazol-1-yl)-2,2'-bipyridine (dmpbipy) was synthesized having a fused N heterocycle ring structure modified from the BTP partitioning ligand, and its extraction performance and selectivity for trivalent actinide cations over lanthanides was evaluated. X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), and time-resolved laser fluorescence spectroscopy (TRLFS) results show that 1:1 complexes are formed, unlike the 1:3 complex for BTP systems. The equilibrium constant for curium complex formation with dmpbipy was determined to be log K = 2.80, similar to that for nitrate. The Gibbs free energy, ΔG(20 °C), of 1:1 Cm-dmpbipy formation in n-octan-1-ol was measured to be -15.5 kJ/mol. The dmpbipy ligand in 1-octanol does not extract Am(III) Eu(III) from HNO(3) but was found to extract Am(III) with limited selectivity over Eu(III) (SF(Am(III)/Eu(III)) ≈ 8) dissolved in 2-bromohexanoic acid and kerosene at pH > 2.4.